The invention concerns a pump station for waste water, said station containing one or several submersible pumps.
A pump station of this type is provided with one or several inlets for sewage water and normally one outlet pipe which is connected to the outlets of the pump or pumps. An example is shown in SE 366 013.
The submersible pump unit is normally arranged to be lowered along so called guides so located, that the outlet of the pump comes to alignment with the rigidly attached outlet pipe when the pump is lowered to its operating position. The connection between the pump outlet and the outlet pipe must be water tight, without the need for bolts or the like. For this purpose a so-called connection unit is fixed on the bottom of the pump station, which unit is provided with a pipe part, attached to the outlet pipe and with a flange to which a corresponding flange in the pump outlet can come into contact. The lower ends of the guides are also normally attached to said connection unit.
The sewage water normally contains a lot of solid bodies such as sludge, which easily collect on the bottom of the pump station. Other bodies such as rugs and fibres are easily wound up on the pump unit and its connection parts. Such sludge banks and rags check the circulation and may cause clogging of the pump inlet.
It is known practice to solve the problem with sludge banks by help of mixing devices which operate intermittently. An example is shown in SE 8900597-9 (U.S. Pat. No. 4,948,342). Other solutions are to install special machines which keep the water in motion.
Another solution to keep the bottom free of sludge is to design it very steep and locate the pump inlet at the lowest point. Examples are shown in U.S. Pat. No. 4661 047 and SE 9300 444-8 (U.S. Pat. No. 5,435,664. However, the problems with elongated objects that stick to the guides, the connection unit etc still remain.